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What is EBT Technology?

Q: I would like to know more about the Pacific Summit woodstove's "Patented Extended Burn Technology". Can you describe it and explain exactly what it does in layman's terms?
Richard

A: Hi Richard,

Like all of our non-catalytic EPA approved stoves, the Pacific Summit, Summit Classic , Alderlea T6 and Summit Insert rely on a secondary burn chamber to reburn the exhaust gases from the primary fire. In order for the fire in the secondary burn chamber to ignite and stay lit, a minimum firebox temperature must be maintained, which requires that an adequate quantity of combustion air be supplied, even when the draft control is turned down to its lowest setting. To address this need, manufacturers of non-catalytic woodstoves typically incorporate a "stop" in the design of the intake draft control, so some air enters both the primary and secondary fire chambers even when the draft control is turned down as far as it will go. This air is delivered to the fire even when it might not be needed, and thus can cause faster than necessary fuel consumption during certain stages of the fire, a problem that is particularly prevalent in models with extra-large fireboxes. The upshot of this situation can be shorter than optimum burn times, and frustrated stove owners who find that they often can't "hold" the fire as long as they might want between refuelings.

The EBT technology was designed to help maximize burn times for wood stoves with large fireboxes. It does this by delivering a burst of combustion air to the fire only as needed to maintain secondary lightoff temperature when the draft control is turned down far enough to create the longest possible burn.

Basically, the EBT device is a pivot plate which is mounted over a hole in the stove's primary air intake plenum so that it covers and uncovers the hole when it pivots. A bimetallic coil is attached to an actuator arm that pivots the plate so that when the firebox begins to cool below a certain point, the coil contracts, and the entire assembly hinges open to uncover the intake hole and provide extra air to the fire. As the burn rate increases from the inflow of oxygen, the firebox heats back up and the coil expands, lowering the base plate back down to seal the hole in the air intake plenum, without changing the original slide draft setting.

Here's another description, without the technical jargon. Let's say you live in an airtight house that has two slide-open windows in it, one operated manually and one automatically. You open the manual window enough to provide an adequate supply of air to your house, but not too much, or the place will be too drafty. As atmospheric conditions and other variables change, it is possible that sometimes your window is not going to be open far enough. If EBT technology was applied to that house, whenever the supply of air from your window opening wasn't adequate, the automatic window would slide open until the optimum ventilation level was achieved, then slide itself shut, returning control of the airflow to the manual window.

When EBT technology is applied to a woodstove, the operator no longer has to worry about whether or not the manual draft control is turned down too low. If the fire should start to smolder from lack of oxygen, the coil senses the resulting temperature drop and automatically hinges the pivot plate open to supply extra oxygen for as long as it takes to re-establish secondary burn temperature. This enables the stove to be operated at lower manual draft control settings without fear of lost heat, excessive creosote formation or smoke pollution.

An Ideal burn cycle should heat the fuelwood to gasification temperature (Stage 1), ignite the volatile gases in the secondary burn chamber, maximize the burn time of the secondary fire until the gases are consumed (Stage 2), then maximize the duration and heat productivity during charcoaling (Stage 3).

Here's how Pacific's EBT helps to achieve the perfect burn.

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